Ballast canister construction



Dec. 10, 1963 R. I. SULZER 3,113,

BALLAST CANISTER CONSTRUCTION Filed Dec. 22, 1958 2 Sheets-Sheet 1 Dec. 10, 1963 R. 1. SULZER 3,1

BALLAST CANISTER CONSTRUCTION Filed Dec. 22, 1958 2 Sheets-Sheet 2 United States Patent BALLAST CANISTER CONSTRUCTION Robert I. Sulzer, Skokie, Ill., assignor to Advance Transformer Co., Chicago, Ill., a corporation of Illinois Filed Dec. 22, 1958, Ser. No. 782,158

2 Claims. (Cl. 220-62) This invention relates generally to the construction of sheet metal containers for electrical components and more particularly is concerned with the construction of a canister for ballasts and the like apparatus.

In recent years the use of fluorescent lamp lighting has increased greatly over common incandescent lamp light ing for many reasons, included in which are increased light for comparable Wattage and power, improved character of the light, etc. The ordinary fluorescent lamp is almost always mounted by suitable socket supports to a sheet metal fixture, which is in some instances used as a starting aid. The sheet metal fixture, in addition to supporting the lamps and sockets, is required to house the additional equipment that may comprise parts of the fluorescent lamp circuit, and in such instances, contains a ballast or ballasts.

Fluorescent lamps are gaseous discharge devices, which not only require high initial potentials to assist in ionizing the internal gases to cause the discharge to commence, but are also negative resistance devices. The flow of current through a gaseous discharge device is not limited by the internal impedance of the device itself, and hence external impedance must be provided. The two functions, namely, the assist to ignition and the provision of impedance to limit current flow are provided in a transformer which steps up the line voltage to the desired ignition value, and which also provides reactance to limit the current flow. This latter quality is achieved through the deliberate building of leakage into the transformer, a technique the details of which are of no concern to this invention. In addition to the transformer, the gaseous discharge circuit may include (and usually does) condensers for their effect upon the reactance for current limitation, their effect upon starting and/or their effect upon power factor.

The transformer and condenser or condensers are enclosed in a metal box or canister, being properlyinterconnected with marked leads protruding from the canister 3,113,694 Patented Dec. 10, 1963 thewindings which includes the transformer and terminal strips, are disposed in the canister together with the conin the bottom of the canister and place the relatively heavy components in this deposit while same is still fluid, pressing them down to cause the compound to flow into the interstices and around the edges. This provides a close bond between the components and the bottom wall, so that heat may be readily transferred through the compound to the wall. The compound is formed of mixtures of pitch or asphalt and silica, in various proportions, and which will be'hard or at least substantially hard at ordinary temperatures at which the ballast is designed to be maintained. Overheating of ballasts can cause this compound to run out.

Thereafter the tops of the components, which have the terminals and connected wires, are covered by means of a strip of insulating material, such as specially treated paper to serve as an insulation from possible grounding or the like. Then the remainder of the canister'is filled with the potting compound, the same being run in under high temperature so that same is of relatively low viscosity. Finally, the metalcover is attached to the open top of the canister and the ballast is complete.

. Ballasts heretofore have had their canisters constructed with flanged end formations at the top of the canister body receiving the electrical components, and the cover plates cooperate with these flanged formations through to enable the proper connections to be made with the ballasts and each unit may contain a transformer, condensers, electromagnetic chokes, small resistors and the like, in various combinations.

Ballasts are required to dissipate heat, since the transformers or other electromagnetic devices have various losses, including eddy current losses, heating due to leakage of flux and the like, and heat is ,of great importance the canister on the side opposite that the use of ears, welding, rivets and the like to enclose the canister. Thereafter the flanged formations are used to fasten the ballast to the metallic plate of a fixture, and in the process, the portion which is so fastened is the cover. Thus, the source of heat comprising the electrical components isseparated from the cover plate by the strip of insulating paper and the space which must necessarily be provided in order to assure clearance of the terminals and connections. Since the most efficient transmission of heat is obtained by transfer to the fixture wall to which the ballast is secured, the ballast construction is such as to prevent most rapid cooling of the ballast.

This invention recognizes that the maximum heat dissipation would be assured if the bottom of the ballast, that is, the part which has the components practically engaged thereagainst, were disposed in fact to face contact with a planar member of the fixture. The primary object of the invention is to achieve this through the provision of a novel form of canister in which the means for fastening the ballast to a metal base or plate are disposed on during the manufacture of the ballast.

. In conjunction with the primary object of the invention,

other objects are concerned with the provision of several novel canister structures which enable the ballast to be operated cooler than heretofore possible, because the heatproducing electrical components are as closely disposed in ballast design. Some heat is also produced by condensers. Underwriters and other organizations concerned with public safety and fire prevention establish certain important requirements relative to the temperature of the ballasts during use thereof, not only under normal conditions but under conditions of emergency as well. The ballast manufacturer is beset with the probleni of assisting the dissipation of heat from, the ballasts'as rapidly as possible for such safety reasons. The dissipation of heat is also a factor in efficient ballast operation as well, and hence it is desirable to keep the ballast cool;

In the manufacture of the ballasts, the assemblage of relative the metal plate member 'to which the ballastis adapted to be secured, as feasible.

7 Other objects and advantages of the invention will occur to those skilled in this art as the description thereof develops hereinafter, not the least of which is the disposition of the leads extending from'the ballast canister spaced from the base or plate to which same is secured,

making them easier to handle and connect, and less likely to become frayed or short-'circuited during installation and .connection of the ballast. The description of the several preferred embodiments is augmented by drawings, the

same being exemplary and not intended by way of limitation, since itis obvious that considerable variation in size, proportion, and minor details is capable of being made which is covered a Z without departing from the spirit or scope of the invention.

In the drawings, in which like characters of reference are used throughout the several embodiments in order to designate the same or equivalent parts or components:

FIG. 1 is a sectional, semi-diagrammatic view illustrating the manner in which a ballast having a canister constructed in accordance with the invention is, secured to the base plate or other metallic surface member of a fluorescent lamp fixture.

FIG. 2 is an exploded perspective view of one end of a ballast canister constructed in accordance with the invention, the opposite end being identical therewith and hence not shown.

' FIG. 3 is a fragmentary developed view of the sheet metal blank from which the open top trough portion of the canister is formed.

FIG. 4 is an exploded perspective view of one end of a modified form of ballast canister construction, the opposite end being identical therewith and hence not shown.

FIG. 5 is an exploded perspective view of one end of a further modified form of the ballast canister construction, the opposite end being identical therewith and hence not shown.

Generally, the invention comprises a ballast canister in which the face of the canister which is to be secured to the sheet metal surface of the fixture is that face which has the electrical components disposed on the interior of the canister as closely engaged thereto as possible. That portion of the electrical components which is most closely engaged to a wall of the canister cannot be the side or face which has the terminals and connections because these must be insulated from the inner surface of the canister, and hence the face opposite that provided with the terminals is that face which is most closely engaged to a Wall. The unobvious solution of the problem is emphasized by the requirements of manufacture, namely, that the components must be disposed initially in the trough portion of the canister with the terminals facing upward, the trough must remain with its open face also upward because it is to be filled with a hot potting compound which is fiuid, the trough must be closed off by the cover member in this position, and flanges or lugs must be provided to enable securement of the entire device to the metal surface of the fixture.

The invention is characterized by the provision of novel sheet metal structures solving the problems described.

In FIG. 1 there is illustrated an installation of a ballast constructed in accordance with the invention, said ballast being shown secured on the interior of a fixture to a sheet metal surface thereof. The ballast is designated and may be presumed to be any one of those illustrated, and the same is provided with the flanges or brackets 12 on opposite ends thereof. There is generally a trough part 14 and a cover part 16, permanently secured together in any manner as will be explained, with the cover part spaced from the fixture wall 18 and hence being on the bottom of the ballast in the, disposition shown. In the specification which follows, the ballast canister will be described-in the disposition it assumes during manufacture, irrespective of the disposition during installation, since the ballast may be disposed on its side, or as in FIG. 1 or reversed from that. The walls of the trough portion 14 will thus be located for purposes of description with reference to disposition of the trough portion 14 during manufacture of the ballast and the wall opposite the open face of the trough formation 14 will be called its bottom wall 29.

Thus in FIG. 1, the bottom wall 20 of the ballast 10 is mounted in face-to-face engagement with the surface 18 of the fixture 22 to provide maximum heat dissipation from the components on the interior of the ballast 10. The components here are the transformer 24 and condenser 26 both of which have their bottom surfaces (related to their positions during manufacture) either directly engaged with the bottom wallZt) of the trough portion 14, or at most separated therefrom by a thin layer of potting compound, say about 19, of an inch in thickness between the wall 26 and the outermost contours of the components 24 and 26. This thin layer is designated 28. The upper surfaces of components 24 and 26 have terminals designated generally 30 to which connecting wires such as 32 are secured and which provide connections for the externally extending leads 34.

There must be sufiicient space between the cover member 16 and the main protuberances of the transformer 24 to permit the clearance for the terminals 30 and leads 32. In addition, a strip of insulating material 36 such as fibre paper is disposed between the transformer 24 and the cover member 16. This means that the heat from transformer 24 will not as readily be conducted to the cover member 16 as it will to the bottom wall 20. The entire ballast is filled with potting compound as shown at 37. The space between tops of components 24 and 26 will be greater than the thickness 28 and may be as much as of an inch and better.

It will be noted that the flanges 12 are co-planar with the wall 20 and hence are opposite to the placement of flanges of ballast canisters heretofore used, the latter having been combined with the cover members of prior structures. The leads 34 extend from the end walls 38 through openings 40 which are provided spaced from the flanges 12 and hence the likelihood of interference between these leads and the fastening means 42 is decreased. Also the leads are more readily manipulated and connected to the circuits of the fixture 22.

In FIG. 2 there is illustrated a ballast canister which is designated 50. It can be used to construct the ballast 10, as can the other ballast canisters shown in FIGS. 4 and 5. Illustrated are the trough portion 14 and the cover member 16, the latter being poised prior to securement to the open top of the trough portion. This construction 50 is characterized by the trough portion 14 being formed of an integral blank of sheet metal, the blank 52 being shown in flattened or developed form before bending, in FIG. 3.

The canister trough portion 14 of FIG. 2 has a bottom wall 20 which is substantially flat to enable face-to-face engagement with the fixture surface 18; vertical side walls 54; and end walls 38, only one of which is shown. The flange 12 in this structure is a continuation of the bottom Wall 20 and is provided with a pair of holes 56 as well as a center open-ended slot 58 which is usual to enable mounting of the ballast. The wall 38 has the openings 40 to accommodate the leads 34. The side walls 54 have upset externally protruding panels 60, a common design feature, and have arcuate protruding formations 62 punched outward of the walls adjacent the top edges thereof. The cover member 16 is a rectangular plate 64 having depending flanges 66 on the opposite edges thereof, these flanges being punched with arcuate openings 68 or other formations designed matingly to engage with the formations 62 to lock the cover member 16 in place upon the trough portion 14 when the ballast 10 is fully assembled.

Inviting attention to FIG. 3, note that the side walls 54 are formed by being bent from the blank 52 at right angle to the bottom wall 20. Thereafter each half of the end wall 38, designated respectively 70 and '72, is bent at right angle relative to the respective side wall end so that the alternately outwardly and inwardly bent slitted formations 74 provided on the respective edges of the halves 70 and 72 will interlock as at 76 to close the end of the trough portion 14. Similar structure could be used as, for example, abutted ends welded together, flanged ends pinched together and the like. The blank also has the flange 12 formed by punching and cutting, which in the blank 52 gives rise to rectangular extensions 7 8 and St) on the bottom edges of the halves 70 and 72 respectively. In forming the slot 58, only a small semi-circle of metal is punched out as at 82, the remainder being slit centrally to provide the ears 84 and 86.

I1 assembly, the extensions 78 and 30 are bent outwardly to overlie the flange 12, and the cars 84 and 86 are curled around the respective extensions to lock same to the flange l2 and strengthen the flange and the slot, to provide good support for the ballast 10 when mounted.

The ballast canister of FIG. 4 has four parts, the cover member 16, the body portion 92 and the end walls 38. The end walls 38 and the body portion 92 are welded or otherwise fastened together to provide the trough portion 14. The body portion W has a bottomwall 29, side walls 54 with panel formations 60, and the ends of the walls are all provided with integral right-angle bent flanges. as shown at 94 and 96. The end wall 38 has an integral right angle bent flange 12 provided on the bottom end thereof formed with slot 58 and holes 56 and has the same openings 40 formed therein for leads adjacent the top edges thereof. There are opposite panels or depressions 98 adjacent the side edges, these panels adapted to align with and be welded to the flanges 96. Suitable means such as upset projections may be provided to facilitate spot weldnig and/ or to align the end wall 38 during assembly. Either or both of the panels 98 and the flanges 96 may be so provided. Also similar means may be used to facilitate welding the flange 94 to thewall 38.

The cover member 16 is again formed as a rectangular plate 64 having depending flanges be but there is an end extension tilt) of the plate 64 which is slotted at 182 to cooperate with the integral tabs 104 provided on the upper edge of the wall 38. When assembled the tabs are bent over to lock the cover member in place. 7

Each end extension 1% may be bent at right angle, downwardly to lie againstthe face of an end wall 38, either before or after assembly. Also shallow depressions or recesses may be formed in the plate d4 as at till to seat the tabs 164 itush with the surface of the plate s4.

The structure lit (FIG. is relatively simple in formation. The cover member. 16 is identical to the cover member 16 of canister 50 of FIG. 2 and hence the side walls 54 are provided with similar formations 62 to cooperate with slots 68. The body 112 is a relatively simple channel formation having the bottom wall 20 integral with the side walls 54. The endwall 258 has the flange 12 with slot 53 and holes 56 and is adapted to be assembled to an end of the channel formation 112 with the integral flanges 116 either inside or outside of the ends of the Walls 54, to which they are respectively welded. Method of assembly of the cover is obvious.

In every case, as described above, the cover member 16 is secured to the respective trough portion 14 at the top of the trough member 14, with the openings 48 adjacent said top end. In every case, also, the flanges 12 are provided coplanar or substantially coplanar with the bottom wall 20 of the canister structure so that when the ballast is eventually mounted to a metal surface 18 oi a fixture 22, the bottom surfaces of the components 24 and 26 will be practically disposed against the bottom wall 2% to provide for maximum dissipation of heat thereto. This wall 26 is that one which will be engaged against the metal surface of the fixture, which is opposite to the arrangement in ballasts heretofore.

It is believed that the invention has been suficiently explained to enable those skilled in the art to understand the same and construct the structures taught thereby, and it is again desired to reiterate that the structures of the invention are capable of wide variation.

What it is desired to secure by Letters Patent of the United States is:

1. In a canister of the character described, a box-like formation having its top open, and being formed of a single integral sheet metalblank, said blank being generally rectangular and having a central section flanked by parallel sections on opposite edges thereof, the parallel sections adapted to be bent at right angles relative the 7 central section, each of'said sections having a pair of opposite ends, the central section comprising the bottom wall and the parallel sections comprising the side walls, each parallel section having rectangular extensions on said opposite ends thereof, the length of which is substantially half the width of the central section, the central section having flange forming extensions on opposite ends thereof, the rectangular extensions adapted to be bent at right angles relative to their respective parallel section and secured end to end to form together a pair of end walls, and the flange forming extensions thereafter constituting bracket means on said box-like formation to secure the same to a surface, the rectangular extensions having transverse strip portions adjacent said flange forming extensions and extending inwardly toward one another, and. said strip portions adapted to be bent at right angles relative to said flange forming extensions to overlie and strengthen same, and be perpendicular to said end walls.

2. In a structure as claimed in claim 1, the flange formingextensions having tabs provided thereon extending inwardly toward one another co-planar with said flange forming extensions and adapted to be bent over said strip portions to lock said strip portions to said bracket means.

References Cited in the file of this patent UNITED STATES PATENTS McCulloch Oct. 28, 1957 

1. IN A CANISTER OF THE CHARACTER DESCRIBED, A BOX-LIKE FORMATION HAVING ITS TOP OPEN, AND BEING FORMED OF A SINGLE INTEGRAL SHEET METAL BLANK, SAID BLANK BEING GENERALLY RECTANGULAR AND HAVING A CENTRAL SECTION FLANKED BY PARALLEL SECTIONS ON OPPOSITE EDGES THEREOF, THE PARALLEL SECTIONS ADAPTED TO BE BENT AT RIGHT ANGLES RELATIVE THE CENTRAL SECTION, EACH OF SAID SECTIONS HAVING A PAIR OF OPPOSITE ENDS, THE CENTRAL SECTION COMPRISING THE BOTTOM WALL AND THE PARALLEL SECTIONS COMPRISING THE SIDE WALLS, EACH PARALLEL SECTION HAVING RECTANGULAR EXTENSIONS ON SAID OPPOSITE ENDS THEREOF, THE LENGTH OF WHICH IS SUBSTANTIALLY HALF THE WIDTH OF THE CENTRAL SECTION, THE CENTRAL SECTION HAVING FLANGE FORMING EXTENSIONS ON OPPOSITE ENDS THEREOF, THE RECTANGULAR EXTENSIONS ADAPTED TO BE BENT AT RIGHT ANGLES RELATIVE TO THEIR RESPECTIVE PARALLEL SECTION AND SECURED END TO END TO FORM TOGETHER A PAIR OF END WALLS, AND THE FLANGE FORMING EXTENSIONS THEREAFTER CONSTITUTING BRACKET MEANS ON SAID BOX-LIKE FORMATION TO SECURE THE SAME TO A SURFACE, THE RECTANGULAR EXTENSIONS HAVING TRANSVERSE STRIP PORTIONS ADJACENT SAID FLANGE FORMING EXTENSIONS AND EXTENDING INWARDLY TOWARD ONE ANOTHER, AND SAID STRIP PORTIONS ADAPTED TO BE BENT AT RIGHT ANGLES RELATIVE TO SAID FLANGE FORMING EXTENSIONS TO OVERLIE AND STRENGTHEN SAME, AND BE PERPENDICULAR TO SAID END WALLS. 